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Animal control systems are well-known. Examples of such a system are found in U.S. Pat. Nos. 5,465,687 and 5,353,744, both assigned to the assignee of the present application and incorporated herein by reference. A transmitter generates a coded Amplitude Modulation (AM) signal that is radiated by a wire-loop antenna. The wire-loop antenna is buried a few inches underground and defines an area in which the animal is to be contained or from which the animal is to be restricted. A receiver mounted on a collar placed around the neck of the animal includes one or more electrodes which are in physical contact with the skin of the animal. As the animal and receiver approach the wire-loop antenna, the receiver detects the radiated AM signal. The received signal is measured and, if the received signal qualifies, a stimulus is applied to the animal. The stimulus may be an audible alert or an electric shock administered to the animal through the electrodes.
While AM-based systems have been relatively successful, their performance suffers from noise, interference and other extraneous problems that may cause a stimulus to be improperly applied to the animal. Therefore, what is needed is an improved animal control system that provides more robust performance and less susceptibility to noise, interference and other reception problems associated with AM-based systems.
An improved system for controlling the movement of an animal employs a Frequency Shift Keyed (FSK) transmit signal wherein a carrier is frequency shifted, or modulated, to either a Mark frequency or a Space frequency. The FSK transmit signal supports the transmission of user-programmable data from a transmitter/control unit to a receiver/stimulus unit typically mounted on a collar placed around the neck of the animal. The FSK transmit signal has a frame structure that includes a leader sequence, a data portion, and a gain test sequence. The leader sequence indicates the start of a frame, the data portion specifies the type and rate of the stimulus applied to the animal, and the gain test sequence is used to equalize receiver response to the Mark and Space frequencies. The FSK transmit waveform improves system performance to thereby lessen the probability of a stimulus being improperly applied to the animal.
The receiver/stimulus unit is battery powered and operates with very low power consumption and having a sleep mode to conserve power. The receiver includes a programmable memory for programming of various system parameters.